The disposal of wastes both from municipal and industrial sources, such as trash, rubbish, garbage, animal wastes, agricultural wastes, and waste of plastic processing operations is rapidly becoming of immense national concern. The cost of disposal ranks third behind public schooling and highways as municipal expense in the United States.
It is estimated that each individual in the country generates between 4 and 6 pounds of waste per day, that the industrial output is equivalent to approximately 5 pounds of solid waste per person per day. Previous methods of mass waste disposal, such as landfill, are becoming impossible, while others such as incineration are costly and result in air pollution problems.
A vast majority of the waste which is presently disposed of contains products which are immediately recyclable back into the economy or products into which the waste can be converted for recycle back to the economy. Directly recyclable constituents are the various metals present, such as aluminum and steel, and glass. For the most part, the organic solid waste fraction is subjected to flash pyrolysis as an operation independent of recovery of the directly recyclable inorganic fraction and any organic portion recovered as pulp. Flash pyrolysis yields solid char, condensible pyrolytic oils and combustible gases.
After pyrolysis of the organic materials, the solid materials in the form of organic char and ash are separated from the gas and liquid constituents. The char, which consists primarily of carbon, and the inorganic ash are fluidized with recycled product gas from the pyrolysis operation and passed through a burner. The burner mixes the char with air to form a combustible mixture that is ignited. The combustion of the char produces additional ash and flue gases. The heat of combustion raises the temperature of the ash to a sufficient temperature for recycling the ash as a heat source in carrying on the flash pyrolysis reaction. At the same time the char is decarbonized to form a flue gas of principally oxides of carbon.
One of the problems in burning the char is to maintain the temperature of the exothermic reaction within certain limits. The ash must be heated sufficiently to carry on the pyrolysis reaction, but must not be heated to a temperature in which the ash becomes molten. It is essential that the ash particles remain in a finely divided state and not coagulate into larger masses, as the particles tend to do if they reach a molten stage.